The present invention relates to improved apparatus and process for forming composite yarns having a central elastomeric or elastic core yarn covered by relatively inelastic cover yarns, the utility and advantages of such composite elastic yarns has been recognized for some time in the textile industry. Such composite yarns provide the advantages of the covering yarn with respect to surface effects, while retaining the extension characteristics of the elastic core yarn during and after fabrication of clothing. Such composite yarns are more capable of withstanding the tension inherent in fabrication and in wearing of cloths made therefrom, than would be the case were the entire yarn made of the inelastic cover yarn.
Numerous prior art methods and apparatus have been proposed for forming composite yarns of the general type contemplated by the present invention. U.S. Pat. No. 3,940,917 to Strachan relates to a composite elastic yarn and process for producing same which involves the stretching of the elastic core yarn, while applying a plurality of inelastic filaments with pressurized fluid entangling means to cover the core yarn. While this arrangement utilizing compressed air to entangle the inelastic cover filaments around the elastic core yarn provides for relatively high speed production of the composite yarn, this arrangement does require substantial expenditures for the compressed air entangling apparatus, which must be constructed with close tolerances in order to carry out the desired tangling characteristics. Also, there is a tendency for the compressed air jets to become jammed up with the yarn, with consequent operational difficulties. U.S. Pat. Nos. 3,078,653 and 3,078,654 to Marshall, disclose systems for manufacturing wrapped elastic yarn, which also utilize a pressurized fluid to aid in the entangling of the inelastic cover material with the elastic core material, which systems also exhibit the above-noted disadvantages of the Strachan system.
U.S. Pat. No. 3,921,382 to Tsujita et al. relates to a method of making a composite covered elastic yarn wherein a multi-filament continuous filament thread is wrapped as a sheath yarn around an elastic core yarn and wherein a false twisting spindle is provided downstream of a heating element for applying a false twist to the composite yarn during the formation thereof. This Tsujita et al. system requires that a twisting spindle and heat setting arrangement be provided for applying the false twist to the composite yarn as it is being produced, thereby requiring the additional expenditures for such false twisting spindle and heating apparatus, not to mention the mechanisms for controlling the tolerances of the false twisting steps. U.S. Pat. No. 3,691,750 also relates to a composite core yarn formed of false twist textured yarns, wherein both the core yarn and the wrapper yarn are false twist textured during formation of the composite core yarn.
U.S. Pat. No. 3,158,985 to Spicer relates to a composite textile yarn and method of making same which includes subjecting the yarn to moist steam under controlled conditions to aid in the formation of the composite yarn. U.S. Pat. No. 3,382,662 to Seelig et al. relates to covered elastomeric yarns which utilize an adhesive layer between the core yarn and the coverng yarn. These last-mentioned arrangements necessarily involve manufacturing expenditures and problems with respect to providing the respective steam conditions, and the adhesive application.
U.S. Pat. No. 3,657,873 to Gibson et al. relates to an arrangement for the formation of a composite elastic yarn with non-elastic cover yarns that are pretextured or false twisted. In this arrangement, the non-elastic yarns and the elastic yarns are first joined at a pair of drawing rollers where the non-elastic yarn twists about the elastic yarn. In this Gibson et al. patent arrangement, the elastic spandex yarn is tensioned sufficiently to provide a predictable contractural force and predictable limit of contraction in the composite yarn. This tension is disclosed as being 16 grams during the joining of the elastic yarn with the non-elastic yarn at the drawing rollers.
It has been found that the composite yarn product obtained by the procedure and apparatus shown in the Gibson et al. patent is unsatisfactory for use as hosiery yarn because the cover yarns will not wrap around the elastic yarn sufficiently and tend to separate from the elastic yarn.